This invention relates to turbine types of power plants and particularly to means for detecting incipient surge of the compressor.
As is well known in the jet engine art, surge is a problem that has plagued the industry since the utilization of axial flow compressors. While there are various theories on surge and the occurrence thereof, suffice it to say, that under certain conditions of engine operation flow separation along the blades can occur causing a pressure pulsation. Without corrective action, this pressure pulsation can be deleterious to the engine and in some cases destructive to the aircraft propelled by that engine. In certain engine applications, surge can be a bigger factor than in other applications and between engine models the surge characteristics are different. Additionally, even in a given engine model, surge may be caused by different factors and may occur at different points along the engines flight envelope.
As for example, U.S. Pat. application Ser. No. 762,763 filed by E. Preti and H. W. Ripy on Jan. 26, 1977 and assigned to the same assignee as this application discloses a surge detector where a single temperature sensor mounted at the compressor inlet detects incipient surge. However, in that application, the only portion of the flight envelope where that detector is operational is when the augmentor is being utilized. Hence, in other portions of the flight envelope, surge can occur without being detected.
Surge detection in the context of this application is the measurement of given parameters that are indications that surge is occurring. Obviously, once surge is detected it is abundantly important that corrective action is taken immediately to correct for the surge. The corrective action does not form a part of the invention, but any of the well-known means can be employed, such as compressor bleed, engine shutdown, engine geometry change and the like.
Additionally, surge detection should not be misunderstood for surge scheduling. Surge scheduling is generally manifested by the engine's fuel control which monitors certain engine parameters and adjusts fuel flow or other variable to operate it below the surge line. Notwithstanding this provision, surge can still occur by aircraft maneuvers, or change in engine characteristics over a duration of time and the like. Hence, surge detection is typically used in addition to the surge prevention scheduling means.
We have found that we can provide surge detection at virtually all occurrences in the engine operation envelope by utilizing a pair of total pressure probes discretely and judiciously mounted in the engine. As for example, actual test results have shown that this invention when mounted in the high compression section of the F-100 engine manufactured by the Pratt and Whitney Aircraft Division of United Technologies Corporation surge was detected for all conditions encountered in the 3 Hertz range. By selection of a suitable switch, it is possible to adjust the hysteresis such that the opening and closing of the switch responds to different .DELTA.P values, hence, maximizing the close time of the switch. This affords the advantage of providing sufficient time in which a logic sensor, either digital or analogue, can sample the detectors so as to give a positive output signal upon an acceptable sample. In this manner, unwanted or false surge detection is avoided.